expression
dual system; double standard
Refers to a system or arrangement where two different standards, rules, or structures coexist, often with a critical nuance of inconsistency or unfairness.
その会社は社員と契約社員で二本建ての給与体系を取っている。
That company has a dual salary system for regular employees and contract workers.
彼の言動には二本建ての基準があるように思える。
His words and actions seem to have a double standard.
Compound of 二本 (two, two long thin objects) and 建て (structure, system). The exact historical derivation is uncertain, but it likely originated from the idea of two pillars or frameworks supporting a single system.